1. Field of the Invention
This invention relates to a data recording and/or reproducing method as well as a data recording medium. More particularly, it relates to a method for modulating and recording digital signals, a method for reproducing recorded signals and a recording medium on which the digital signals are recorded.
2. Prior Art
There are a variety of different types of apparatus for recording and reproducing data on a recording medium, operating on various recording/reproducing principles or utilizing recording media having various outer shapes.
In general, data recording media can be classified according to the operating principle, such as the magnetic and/or optical recording/reproducing principle, and also according to the outer shape, such as tape, card, or disc shaped recording media.
For example, there are disc players dedicated to reproduction, such as CD players for reproducing a so-called compact disc (CD) on which audio signals such as voice or musical sound are previously recorded in a digitized form.
In a compact disc (CD), as shown in FIG. 1, a data format having 98 frames as one subcode block is standardized, wherein each frame is constituted by a 24-bit sync signal, supplied as eight to fourteen modulation data, in which 1-symbol/8-bit signals are converted into data of 14 bits (L channel bit) constituting 1 symbol of subcode, i.e. one symbol being composed of 14 bits, 32 symbols of data, such as two sets of 12 symbols of play data and 4 symbols of parity bits, with each symbol being composed of 14.times.32 bits, and with three merging bits between the adjacent symbols. Thus each frame includes the sum total of 588 bits. The absolute address of each subcode block is given by the Q-channel signals of the above subcode and the data such as the play data are processed at intervals of one subcode block.
In the EFM in the above described compact disc (CD), modulation is so made that the number of the consecutive "0" bits in a concatenation of the 14 bit or 1 symbol data and 3 merging bits is not less than 2 and not more than 10. On the other hand, the digital sum value (DSV) is counted continuously from the start position of the recording data and the merging bits of the bit pattern according to or consistent with this DSV value are given to control the above DSV.
A similar technique is disclosed in, for example, the U.S. Pat. No. 4,539,691 owned by the present Assignee.
In CD-ROMs, as shown in FIG. 2, wherein the left and right channel digital audio signals recorded on the compact disc (CD) are alternately connected at intervals of one word (2 symbols=16 bits) so as to be treated as one channel of serial data and the CD is treated as a data storage device, a header section and sync signals are annexed ahead of each subcode block or 98-frames of data in the CD data format, such that each sector or block is constituted by 2 K bytes of data.
Since the conventional CD player is dedicated to reproduction, attempts have been made to develop a data storage medium and a recording and/or reproducing system making use of the data storage medium, such as a so called "write once compact disc" (referred to as a "CD-WO") or an erasable compact disc (referred to as "CD-erasable") or "CD-RAM". This CD-WO or CD-erasable makes use of a magneto-optical disc which is formed by a rewritable magneto-optical recording medium and which is interchangeable with respect to the CD or CD-erasable, as disclosed in our co-pending U.S. patent application Ser. No. 102,009 filed on Sept. 28, 1987.
In the CD data format, as described hereinabove, the DSV is counted continuously from the start position of the recording data, and the merging bits of the bit pattern consistent with the DSV value are afforded to control the DSV, so that data writing or rewriting cannot be made. On the other hand, in data storage such as CD-WO or CD-RAM, it is necessary to control the data efficiently.